In a copying machine or a printer using an electronic process, it is well known that a toner image formed on a photosensitive drum is transferred to a transfer material, and then, a toner image molten by a fixing apparatus including a heat roller and a pressure roller is fixed to the transfer material.
At this time, there is known a method of detecting a surface temperature by using a detecting element brought into contact with a surface of the heat roller and controlling a temperature of the heat roller. However, the contact temperature detecting element may degrade the surface of the heat roller due to sliding and has a problem that a service life of the heat roller is reduced. In addition, responsiveness of the detecting element is degraded due to surface degradation, whereby a temperature may be incorrectly detected.
Further, it is known to use a temperature detecting element which senses a red infrared ray radiated from a heat roller to detect a temperature of a heat roller in a non-contact manner.
However, at a radiation rate of the red infrared ray from the heat roller detected by a non-contact temperature detecting element, the surface of the heat roller is gradually degraded by the heat roller coming into contact with a transfer material which holds a toner. Thus, a deviation occurs at the life beginning of using the heat roller and at the life end of using the heat roller. In addition, the degradation of the surface of the heat roller is different depending on type or size of a transfer material passing through paper, and thus, a deviation occurs in a longitudinal direction of the roller at a red infrared ray-radiation rate. That is, a time for a temperature detected by the non-contact temperature element to reach a set temperature is delayed due to a change of red infrared ray radiation.
For example, in Jpn. Pat. Appln. KOKAI Publication No. 2004-21079, there is disclosed a fixing apparatus for pinching, transferring, and heating a recording agent having an image carried by a nip formed of first and second fixing members. In this fixing apparatus, first and second temperature sensing means each have a heat source in the vicinity of the nip and are allocated in non-contact with the heat source. In the case where a difference in sensing temperature between the first and second sensing means is obtained as a predetermined value or more, the heat source is stopped or the heat source is controlled at a lower temperature than a control temperature when fixing is executed. There is disclosed a technique of allocating the first temperature sensing and the second temperature sensing means at their different positions in the longitudinal direction of the nip.
In addition, in Jpn. Pat. Appln. KOKAI Publication No. 2003-017221, there is disclosed a heating apparatus comprising: a heat roller heated by a heating source; external heating means for carrying out heating from at least the outside of the heat roller serving as the heating source; and a safety temperature sensing member which shuts out power supply to the external heating means. The publication discloses a technique of allocating the safety temperature sensing member on a heating region at which the external heating means heats the heat roller and covering a gap between the safety temperature sensing member and a coil serving as the external heating means with a magnetic force shield member.
Further, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-289572, there is known an invention relating to an apparatus comprising: a thermal fixing section which fixes an image onto a recording medium by heating; first temperature detecting means for detecting a temperature of a position through which the recording medium on the thermal fixing section does not pass; second temperature detecting means for detecting a temperature of a position through which the recording medium on the thermal fixing section passes; determining means for determining whether or not a temperature difference between a detected temperature by the first temperature detecting means and a detected temperature of the second temperature detecting means is at a predetermined level or higher; and control means for shielding power supply to the thermal fixing section in accordance with affirmative determination of the determining means.
In addition, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 10-031390, there is known a technique using non-contact temperature detecting means which has self temperature detecting means, thereby recognizing a temperature T of the heat roller as a multi-order formula between a self temperature output T1 and a sensor output T0 of a non-contact temperature sensor, the sensor output being sensed and outputted according to the self temperature output and a heat roller temperature which is non-sample, and controlling the temperature of the heat roller.
Moreover, Jpn. Pat. Appln. KOKAI Publication No. 9-281843 discloses an electro photography apparatus having a non-contact sensor which senses a temperature of a heat roller in a non-contact manner, the apparatus controlling the temperature of the heat roller by a sensor output of the non-contact temperature sensor. The electro photography apparatus has means (fan) for supplying air from a pair of image carriers to a fixing apparatus, and the non-contact sensor is allocated so as to include at least a part of the sensor in air between the fixing apparatus and each of the image carriers.